Basics of Microscopy and Observation

Learning Objectives:

1. Describe the methods of tissue preparation used in histological examination

2. Describe the chemical basis for histological staining

3. Understand the principles of light microscopy and electron microscopy

SLU Slide 97: Ovary

Iowa Virtual Slidebox: ovary-infant (298) (embedded below)

Ova are large, round cells found easily near the periphery of the ovary. Begin by examining a slide with your naked eye to identify the outside of the ovary. Move the slide to the microscope stage, and confirm your observation.

 

Study the ovum further using increased magnification. Can you differentiate the nucleus from the cytoplasm? Can you identify the nucleolus? It is usually round and intensely purple. If you do not see one in this particular ovum, move on to another.

Can you distinguish the cell membrane of this ovum? What about in other cells?

You may be able to distinguish the cell membrane of an ovum as the outer limit of the cell’s cytoplasm. In other cells it may be harder because the cells are smaller and less distinct.

Make a sketch of an ovum, illustrating the cytoplasm, size and shape of nucleus, and position of the nucleolus. Alternatively, take a screenshot of an ovum and label the same features.

Your sketch should demonstrate a large, spherical cell with a large, spherical nucleus that is centrally located or slightly off to one side, and a prominent, centrally located nucleolus. 

SLU Slide 16: Anal Canal

Iowa Virtual Slidebox: Anus-rectoanal junction (123).

Examine this slide and note that one side of the tissue is stained an intense blue/purple, while other regions are more lightly stained. Which stain more heavily imparts the intense purple color to those cells? What does this tell you about its chemical makeup? What part of the cell typically stains this color?

Hematoxylin imparts the darker purple color to cells that are basophilic. Basophilic cells attract basic particles because they are acidic. The nucleus is one region of the cell that typically stains strongly with hematoxylin and other basic dyes because of its acidic structure (nucleic acid).

What about the bright pink color? What does that tell you about those cells and their chemical makeup?

The bright pink color is imparted by Eosin. Cells and cell structures that stain heavily with Eosin are said to be Eosinophilic because they attract Eosin and other acidic dyes. That means that these structures are basic. Cytoplasm typically stains strongly with Eosin.

SLU Slide 74: Esophagus

Iowa Virtual Slidebox: Esophagus (111)


Examine this slide with the naked eye before placing it on the microscope stage, or at low magnification before zooming in if examining virtually. What can you tell about how this organ was sectioned? Draw a diagram below of the esophagus, indicating how this particular section was obtained.

The esophagus is a tubular structure, and this section is arranged in a circle. This tells us that this section is a transverse section of the Esophagus.

Look at the internal and external surfaces of this tissue. What gross observations do you notice? How is this tissue organized? (Use terms like, “basophilic” “acidophilic”, “high/low density of cells,” or anything else that pops out at you).

This section of the esophagus shows a more basophilic layer near the center (lumen) of the organ, and  more Eosinophilic/lightly staining layers near the outside. A particularly lightly staining layer lies in between the center layer (epithelium) and the outer layers (muscularis).  You can see numerous small cells on the luminal surface, but near the outside the cells are more sparse. You may also notice that there seem to be several layers of tissue that are clumped together (these clumps represent muscle layers).  

SLU Slide 11: Esophagus

Iowa Virtual Slidebox: Esophagus (198)

Examine this slide with the naked eye before placing it on the microscope stage, or at low magnification before zooming in if examining virtually. What can you tell about how this organ was sectioned? Draw a diagram below of the esophagus, indicating how this particular section was obtained.

This is a longitudinal section of the esophagus.

Look at the internal and external surfaces of this tissue. What gross observations do you notice? How is this tissue organized? (Use terms like, “basophilic” “acidophilic”, “high/low density of cells,” or anything else that pops out at you.)

Many of the same observations as above hold for this section as well. The outer layer is particularly sparse in this section, and the layers of muscle tissue may be more apparent. Don’t worry about the name of the layers for now, but hone your observational skills to see if you can see differences in the direction of the cells and surrounding fibers.